I believe I had the same injury NBP. Its in the lower back I think it is your muscle (kinda near the side, lower back..but still near spine). I had to do a lot of research on my own. The exercises I wrote here were the most helpful.
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Lower back pain is combination of tension in your hamstring and calf muscles, and possibly weak abdominal support (your abs help support your back).
I found the following stretches help the most. It is important to do these before you go to bed and when you wake up:
Hamstring stretch-
-lie on your back
-bring one knee to your chest
-use your hands to lightly press your leg to your chest
(keep your head back while you do this)
-Count to 20
Repeat with other leg, do each leg about 3 times
Reason for this stretch: The hamstring muscle extends to the back. Any tension in the hamstring will tighten the lower back as well. Doing solely back stretches will not help (I've gone through it).
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After doing the hamstring stretch above, I usually follow with this lowerback / abdominal muscle stretch:
Reason: This stretches the abdominal muscles and the lower back.
I call it the "
Walrus stretch"
-Lay down on your stomach
-place hands near your shoulders, palms on ground
-Gently push your self up (keeping your legs straight, flat on ground) with your hands.
-Hold for 15-20 seconds
-Gently ease down
This stretches your lower back and your abs.
*Don't over stretch the back, do the exercise gently
*I usually ad in gentle twists from middle to side, back to middle then other side.

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Following the previous two stretches I did these exercises:
Reason for these exercises: lightly strengthens your lower back
Locust pose (a yoga pose)
-Lie on your stomach
-extend your hands forward above the ground, but not above your head
-keep your head looking forward
-raise your legs in the air as well, even with the arms
-count to 15-20 seconds, repeat exercise twice
The picture has the arms behind the head. It doesnt really matter how the arms are.
Scorpion pose (another yoga pose)
-Repeat the steps for the Walrus stretch, but do not ease yourself down yet.
-At the end of the Walrus stretch, raise your legs up (Knees to feet portion of your leg) at a 45 degree angle
-Hold for 15 seconds
-Repeat this twice
I doubt you are flexible enough to get your feet to your head. Dont try. Just do as I said above. The picture is just to give you an idea of the stretch:
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Cat pose
-Do the stretch in reverse too (arching your back down). Don't arch it too much, as it can cause strain.
-take a look at the related videos, I saw some that could help too.
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Abdominal exercises:
I found crunches to be fine. However, I recently found that it can be harmful while your back is still recovering. So here is some info that has some ab strengthening alternatives:
Source:
http://www.bigbackpain.com/back_exercises.html
The Bridge: Strengthens several core muscle groups - buttocks, abs, back
Lie flat on back; bend knees at 90-degree angle, feet flat on floor. Tighten abs. Raise buttocks off floor, keeping abs tight. Shoulder to knees should be in straight line. Hold for a count of five. Slowly lower buttocks to floor. Repeat five times.
The Plank: Strengthening exercise for back, abs and neck (also strengthens arms and legs)
Lay on stomach, place elbows and forearms on floor. In a push-up position, balance on your toes and elbows. Keep your back straight and legs straight. (Like a plank) Tighten abs. Hold position for 10 seconds. Relax. Repeat five to ten times. If this exercise is too difficult, use balance on your knees instead of your toes.
A picture of the plank stretch:
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Also try this site for abdominal strengthening:
http://www.lower-back-pain-answers.com/ ... cises.html
Some useful charts:
http://backpainphysicaltherapy.net/wp-c ... cises1.gif
http://www.doctorvlad.com/lowerbackpain ... _guide.jpg
**As a side note, it would couldn't hurt to not only stretch your hamstring muscles, but your other leg muscles as well.
-Updated expired pictures and added links to useful charts.-